Peng, a Wimbledon doubles champion in 2013, posted allegations against Zhang Gaoli on Chinese social media site Weibo last week.
The post, along with all of Peng's other content, has since been removed from the site.
Multiple reports suggested the 35-year-old had subsequently not been seen or heard from, and the Women's Tennis Association (WTA) called for a full investigation into the matter.
There has so far been no response from the Chinese government to the allegations.
However, a spokesperson for the ministry of foreign affairs informed reporters he was not aware of the situation.
"I have not heard of the issue you raised," the spokesperson said via a widely released statement. "This is not a diplomatic question."
Now Osaka, a four-time major champion and one of the biggest names in the sport, has used her platform to question the situation.
"Hey everyone, not sure if you’ve been following the news but I was recently informed of a fellow tennis player that has gone missing shortly after revealing that she has been sexually abused," Osaka wrote in a statement published to her official Twitter account.
"Censorship is never ok at any cost, I hope Peng Shuai and her family are safe and ok. I'm in shock of the current situation and I'm sending love and light her way."
Osaka concluded her post with the hashtag: "#whereispengshuai".
On Sunday, WTA chairman Steve Simon addressed the matter in a statement that said: "The recent events in China concerning a WTA player, Peng Shuai, are of deep concern.
"As an organisation dedicated to women, we remain committed to the principles we were founded on – equality, opportunity and respect.
"Peng Shuai, and all women, deserve to be heard, not censored. Her accusation about the conduct of a former Chinese leader involving a sexual assault must be treated with the utmost seriousness.
"In all societies, the behaviour she alleges that took place needs to be investigated, not condoned or ignored. We commend Peng Shuai for her remarkable courage and strength in coming forward.
"Women around the world are finding their voices so injustices can be corrected.
"We expect this issue to be handled properly, meaning the allegations must be investigated fully, fairly, transparently and without censorship.
"Our absolute and unwavering priority is the health and safety of our players. We are speaking out so justice can be done."
Osaka's comments follow on from men's world number one Novak Djokovic expressing his concern over the situation when speaking to the media earlier this week.
Djokovic said: "I don't have much information about it. I did hear about it a week ago.
"Honestly, it's shocking that she's missing, more so that it's someone that I have seen on the tour in the previous years quite a few times.
"It's not much more to say than hope that she will be found, that she's OK. It's just terrible. I can imagine just how her family feels that she's missing."